A post-ep for Valkyrie so spoilers spoilers everywhere. There might be an epilogue at some point.

He starts to feel the cold after two and a half hours.

After five he starts shaking.

After six it's uncontrollable. He's cold and he's shaking and everything he tries to hold he drops.

At seven and a half, Kate is given permission to take him home. It feels like they're sending him back to die.

She wraps him up in blankets, deposits him on the couch, and goes about fixing some food pretending like she's okay. She's not okay. He's not okay. None of this is okay. They're supposed to get married. He's supposed to get choked up when he sees her walk down that aisle, and she's supposed to be given away by her father. There was supposed to be a honeymoon on a beach in some hot, faraway place where Kate wears either a bikini or nothing else.

There was supposed to be children. A little boy with his father's smile and his mother's sense of adventure. And a girl. Boisterous and loud and demanding and the worst mix of both of them. A dog, and a house and a white picket fence with a porch swing.

Instead he's getting a national conspiracy and a death sentence.

At ten hours, he's convinced he can feel his body shutting down. His head feels heavy and his heart is going too fast and he can't breathe and he's convinced this is it that this is the end and he can't breathe there's something clogging in his throat and is it his heart he thinks it's his heart it's fighting its way out of a dying mans body-

"Castle, look at me." Kate. Oh, god. Kate. He can't leave – he has to stay – "Castle, open your eyes and look at me."

"I can't –"

"Yes, you can. Just open your eyes." She's got her hands on his, an anchor, warm and safe and secure and keeping him tethered to the sofa, and he opens his eyes.

He hadn't realised how dark it had gotten, or maybe that's just the shadowy tendrils of death reaching out for him. "Kate, I can't…"

"You're having a panic attack. You just need to breathe. In through your nose, out through your nose. Castle, please."

"Are you asleep?"

"No." she replies in a whisper.

"You should sleep."

Kate is silent for a moment, a baited pause that is weighted with all the events of the day. "I'm scared. I'm scared that I'll go to sleep and you'll stop breathing."

He fumbles in the dark for her hand, entwines their fingers. He realises he's not the only one shaking. "I'm scared too."

He doesn't remember the ambulance.

He doesn't remember the time his heart stopped.

With seven hours left, Beckett wants to curl up in a ball and cry. She wants to break down in a corner and ignore the fact that her fiancé is in a coma. Single digits.

Except she can't, because there's still the chance that she could save him.

Find the person who set Jack up.

Get the antidote.

Don't dwell on the fact there might not be one.

McCord gets the break. The idiot had been watching the locker, caught on security camera. Vinn McKenna.

She doesn't get the satisfaction of interrogating him though. Too close. Far too close. Instead, she goes to the hospital and Castle's bedside, leaves McCord to do her job.

Two hours left, and she's starting to give up hope. They've got the guy. They just don't have an antidote. Castle's stats are stable, if a bit weak. He's still cold to the touch, his skin like marble underneath her fingers. This is all wrong. It's so wrong. Castle, such a vibrant, excitable, man. Fidgety. Can't keep still. And now he's as still as stone, save the flutter of his chest as the machine breathes for him.

Oh, she's scared.

Every knock on the door makes her jump. It's never McCord. Always doctors. Just a check-up. He's doing fine, they say. He's doing fine, like in one hour his heart won't fail and he won't plummet head long into a grave he shouldn't inhabit for another forty years. Her own heart is stammering in her chest now. An irregular beat that matches the terrifying thoughts in her head.

It was hard enough losing her mother. It took thirteen years of her life, thirteen years of work work work and nothing left for her. And Castle gave everything back. He gave her everything. Hope and renewal and a chance to live her life the way her mother would want her to. The way teenage Katherine Beckett always dreamed off.

What's it going to cost her, losing Castle too?

What does she do then?

Half an hour and she's standing at the window, looking out at the DC skyline with an ever present sense of doom on her shoulders.

She was supposed to marry him.

She doesn't knock. In true McCord fashion, she just barges in, tearing through Kate's bubble of despair and defeat, and takes no time in marching over to Castle's IV and jamming a needle in.

Five minutes.

Four minutes, and no response.

Three minutes, his heart rate goes up. His blood pressure stops dropping.

There's hope.

Two minutes.

One minute.

He wretches, chokes on the ventilator as he emerges from whatever dark depths he'd sank into. Kate is across the room in an instant, cradling his hand in hers, whispering to him, just to stay still. It'll be okay. He's okay.

They're all going to be okay.